Screening apparatus



June 4, 1963 M. M. CANNON ET AL 3,092,578

SCREENING APPARATUS Filed Jan. 16, 1959 2 Sheets-Sheet 1 June 4, 1963 M. M. CANNON ET AL 3,092,578

SCREENING APPARATUS Filed Jan. 16, 1959 2 Sheets-Sheet 2 United States Patent 3,092,578 SCREENING APPARATUS Madison Mott Cannon, Wellesley, Mass., George McKinstry Dick, Sherhrooke, Quebec, Canada, and Salomon Maury Salomon, Sharon, Mass, assignors to Bird Machine Company, South Walpole, Mass., a corporation of Massachusetts Filed Jan. 16, 1959, Ser. No. 787,291 2 Claims. (Cl. 2l0304) This invention relates to a screening device for liquid suspensions and pertains more particularly to a screening device for use with suspensions of fibers or other solid particles, for example paper pulp.

Screening devices for screening liquid suspensions such as paper pulp have long been employed in which moving vanes or foils are mounted for travel across the face of the screens in close proximity thereto for the purpose of preventing clogging of the screen openings by the paper fibers or other solid particles of the suspension which is being screened. One portion of the suspension passes through the screen while the other is retained. In the case of paper pulp, the desired material passes through the screen while undesired impurities such as dirt particles, wood slivers, and the like, being too large to pass through the screen openings, are passed through a waste outlet.

It has been found in the operation of such screening devices that occasionally very large solid objects may be present in the liquid suspension accidentally, as for example large pieces of metal such as nuts or bolts or pieces of broken glass, rock, etc. These relatively large objects occasionally become wedged between the face of the screen and the moving bar of foil used to clear the apertures of the screen plate, leading to breakage of the screen plate or damage to the bars or foils or both.

One object of the present invention is to provide a simple and inexpensive construction for removing such large and heavy contaminating objects from a liquid suspension prior -to its passage through the screen plate.

Another object is to provide a generally cylindrical inlet portion for a cylindrical screening device, which inlet portion is provided with a trap for receiving and accumulating such large and heavy contaminating objects and for preventing them from reaching the screen plate.

Other and further objects will be apparent from the drawings and from the description which follows.

In the drawings:

FIG. 1 is a view in elevation, partly broken away and in section, of one embodiment of the present invention;

FIG. 2 is a View in horizontal section taken along line 22 of FIG. 1;

FIG. 3 is a view in section, partly broken away, taken along line 3-3 of FIG. 2;

FIG. 4 is a view corresponding to FIG. 3 showing a modified embodiment of the invention; and

FIG. 5 is a broken-away view in horizontal section showing another embodiment of the invention.

In accordance with the present invention it is proposed to employ a screening device which may contain a pair of spaced, concentric, generally cylindrical screens between the opposing faces of which a stream of liquid suspension such as paper pulp is introduced, the acceptable portion of the suspension passing through the screen faces while the unacceptable portion containing the undesired particles is passed out to waste through a separate outlet. The inlet portion of the device, which conducts the stream of liquid suspension to the screens, is generally circular in cross section, having in the preferred embodiment which is illustrated a generally cylindrical outer wall. The stream of liquid suspension is introduced into the inlet portion tangentially thereof and a trap is provided which opens outwardly from the wall of the inlet portion in the path of the advancing stream of suspension. The relatively large and heavy objects which might damage the screen itself are thrown by centrifugal force into the trap, which retains them until they can be removed.

In the preferred embodiment of the invention as shown in the drawing, there is provided a main frame 10 on which is mounted a hollow inner housing 12, preferably generally cylindrical, within which are supported the main journal bearings 14, 16 in which is journaled a drive shaft 18. The upper end of housing 12 is sealed by a closure 20 which is provided with a stufiing box 22 through the upper end of which shaft 18 projects. Stuffing box 22 serves to seal the space above closure 20 from the space within housing 12. The lower end of shaft 18 is provided with a multiple V-belt pulley 24 afiixed thereto which may be driven by means of a conventional belt drive from any suitable source of power, for example an electric motor (not shown). Fixed to the upper end of shaft 18 above closure 24) is a hub 26 to which is bolted a spider 29 the radially projecting arms of which serve to support and drive the clearing foils or bars as described below.

Two spaced cylindrical screens 30, 32 concentric with shaft 18 are provided forming a screening chamber between them having an open upper end, inner screen 30 being supported from the upper end of housing 12 by a flange 34 which extends radially outwardly from the upper end of housing 12. Screen 30 forms one wall of inner receiving chamber 36 into which the acceptable suspension is discharged after passing through screen 30.

An annular channel 38 of U-shaped cross-sectional configuration is located at the bottom margin of inner screen 30 and is supported by a plurality of legs 34 on main frame 10. One leg is hollow, serving as an outlet 40 leading to waste. Outer screen 32 is mounted on the outer rim of channel 38, its upper end being supported by a flange 42 which in turn is supported by the generally cylindrical outer wall 44, d5 of the outer receiving chamber 46 which serves to receive acceptable suspension after its passage through screen 32. Outer Wall 44, 45 is supported by a bottom wall 48, spaced below the bottom of trough 38, which seals the lower ends of receiving chambers 36 and 46 and conducts material from the receiving chambers to the main outlet 5% for the accepted stock.

From the outer ends of the spider arms 29' depend hangers 52 which in turn support clearing foils or bars 54, 54, 56, 56, each of which is of streamlined crosssectional configuration having a smoothly rounded front merging into a tapering tail. Foils 56, 56 are disposed adjacent the face of inner screen 30 while foils 54, 54'

are disposed adjacent the face of outer screen 32. The direction of rotation of shaft 18 is such that the foils move in a clockwise direction as seen in FIG. 2. As the foils sweep across the face of the screens, a negative pressure is developed between the foil and the adjacent screen surface, serving to dislodge from the apertures of the screen any particles or fibers which have accumulated at the aperture and tend to obstruct the flow through it.

The inlet portion of the screen disposed at the upper end of the device as seen in FIG. 1, has a generally cylindrical outer wall 60 which is generally circular in crosssectional configuration, as seen in FIG. 2. Outer wall 6% and wall 44 of the screen together define an annular passageway. A feed means for this inlet portion is provided by a flanged opening 62 communicating with the inlet portion through outer wall 65 serving to introduce the stream of liquid suspension tangentially into the an nular space between walls 44 and 69. A lid or cover 64 is provided to permit operation of the device with the stream of liquid suspension under positive pressure if desired.

The trap of the present invention communicates with the annular inlet portion between walls 44 and 60 through outer wall 60 by means of a flanged fitting 66 which preferably extends substantially tangentially from wall 60 in the same direction as the direction of flow of the stream of liquid suspension. Flanged fitting 66 is spaced from flanged opening 62 by an angular distance of at least 90 in the direction of advance of the stream of liquid sus pension and preferably is approximately 180 from opening 62.

The trap consisting of a chamber 68 is connected to fitting 66 by means of an L 70 and is provided with shut-01f valves 72, 74 at its top and bottom.

In operation of the device, the stream of liquid suspension such as paper pulp is introduced, preferably under pressure, through flanged opening 62 and flows in a clockwise direction through the annular passageway between walls 44 and 60, as seen in FIG. 2. Any heavy objects such as pieces of metal, rock or the like are thrown outwardly against wall 60 as the stream advances until as they reach flanged fitting 66 they are no longer constrained into a circular path by an outer wall 60 and are free to move straight ahead into the upper portion of L 70, the only retarding force being that furnished by the resistance of the liquid suspension which fills the fitting and the L. The liquid suspension overflows wall 44 during its passage about the inlet portion, Wall 44 together with flange 42 serving as a weir. The liquid suspension then flows downwardly through the annular slot between screens 30 and 32 and is subjected to a screening action in the usual manner, the accepted suspension leaving the device through outlet 50 while small particles of dirt and the like which have been removed by the screens exit through outlet 40.

During normal operation of the device, valve 72 at the top of trap 68 is left open while valve 74 at the bottom is kept closed, thus permitting the pieces of rock, metal or the like which have entered L 70 to fall into trap 68. At suitable intervals during operation of the device, valve 72 is closed and valve 74 is opened to permit the accumulated trash to be removed, whereupon the valves are returned to their original setting to permit continued operation of the device.

It has'been found that the outlet fitting 66 may be located adjacent the bottom of the annular inlet portion between walls 44 and 60, as shown in FIG. 3, and that the effectiveness of, the trap arrangement is improved by providing an inwardly projecting lip 80 adjacent the top of wall 60 so as to deflect downwardly any objects of trash which may be riding along wall 60 carried by the advancing flow of liquid suspension. However, it is not es sential that the opening to fitting 66 be so located; in-

deed, it preferably is elongated in a vertical direction, ex

tending somewhat higher in the inlet portion as shown at 67 in FIG. 4 in order to be capable of receiving trash of varying density. In addition, instead of providing an inwardly projecting lip 80 on the outer wall, it is also effective to incline the inner face of wall 60 inwardly toward the top as shown in FIG. 4, this construction also urging the trash or debris downwardly toward the opening to fitting 66 and tending to prevent it from being carried upwardly over the top of inner wall 44.

Although foils S4, 56, in the embodiment shown, move in a clockwise direction (in the same direction as the flow of liquid suspension), it is also possible to obtain satisfactory results by reversing each foil, as shown in FIG. 5, and reversing the direction of rotation of pulley 24 and the structure supporting the foils so that the foils are moving in a direction countercurrent to the stream of liquid suspension.

The foregoing trap construction has been found to be highly elfective in reducing accidental breakage of or shaft in vertical position and with the inlet portion at the top, but it will be understood that it may also be operated with the shaft in horizontal position if desired, particular 1y when the supply of liquid suspension is under pressure. In whatever position the device is mounted, it is desirable to have trap 68 located below fitting '66 so that objects will be retained in the trap by gravity.

Although specific embodiments of the invention have been described herein, it is not intended to limit the invention solely thereto, but to include all of the obvious variations and modifications within the spirit and scope of the appended claims.

What is claimed is:

1. A device for screening liquid suspension having a screening chamber open at its upper end and enclosed by a generally vertical cylindrical screen wall, means for clearing the screen mounted within said screening chamber and adjacent the inlet face of the screen for movement .along the periphery of said passage and extending tangentially outwardly from said passage through the outer Wall thereof and communicating with the space between said two imperforate walls and spaced below the upper margin of said screen wall, said trap outlet being arranged with respect to the tangential flow from the inlet to receive solid objects thrown outwardly by centrifugal force during flow of said suspension through said passage and to prevent said objects from entering said screening chamber.

2. A device as defined in claim 1 in which said trap is spaced from said inlet opening by a peripheral distance of at least along said arcuate passage.

References Cited in the file of this patent UNITED STATES PATENTS 630,363 Krause Aug. 8, 1899 762,867 Allen June 21, 1904 1,471,807 Roosevelt et al ()ct. 23, 1923 1,751,689 Enz et al. Mar. 25, 1930 r 2,068,048 Adams Jan. 19, 1937 2,670,849 Dummire Mar. 2, 1954 2,747,741 Jacobson May 29, 1956 2,975,899 Cannon et al Mar. 21, 1961 FOREIGN PATENTS 450,810 Canada Aug. 31, 1948 

1. A DEVICE FOR SCREENING LIQUID SUSPENSION HAVING A SCREENING CHAMBER OPEN AT ITS UPPER END AND ENCLOSED BY A GENERALLY VERTICAL CYLINDRICAL SCREEN WALL, MEANS FOR CLEARING THE SCREEN MOUNTED WITHIN SAID SCREENING CHAMBER AND ADJACENT THE INLET FACE OF THE SCREEN FOR MOVEMENT THEREACROSS, SAID DEVICE HAVING AN INLET PORTION IN THE FORM OF A GENERALLY ARCUATE PASSAGE HAVING TWO GENERALLY CYLINDRICAL RADIALLY SPACED IMPERFORATE WALLS SURROUNDING AT LEAST A PORTION OF SAID CYLINDRICAL SCREEN WALL ADJACENT TO AND BELOW ITS OPEN END, SAID PASSAGE COMMUNICATING WITH SAID CHAMBER SOLELY OVER THE INLET OPENING DISPOSED BELOW WALL, SAID PASSAGE HAVING AN INLET OPENING DISPOSED BELOW THE UPPER MARGIN OF THE SCREEN WALL SERVING TO INTRODUCE A STREAM OF SAID SUSPENSION TANGENTIALLY INTO SAID ARCUATE PASSAGE, AND A TRAP OUTLET SPACED FROM SAID INLET OPENING ALONG THE PERIPHERY OF SAID PASSAGE AND EXTENDING TANGENTIALLY OUTWARDLY FROM SAID PASSAGE THROUGH THE OUTER WALL THEREOF AND COMMUNICATING WITH THE SPACE BETWEEN SAID TWO IMPERFORATE WALLS AND SPACED BELOW THE UPPER MARGIN OF SAID SCREEN WALL, SAID TRAP OUTLET BEING ARRANGED WITH RESPECT TO THE TANGENTIAL FLOW FROM THE INTLET TO RECEIVE SOLID OBJECTS THROWN OUTWARDLY BY CENTRIFUGAL FORCE DURING FLOW OF SAID SUSPENSION THROUGH SAID PASSAGE AND TO PREVENT SAID OBJECTS FROM ENTERING SAID SCREENING CHAMBER. 